package com.itheima.zhuanhuan;

import java.util.HashMap;
import java.util.HashSet;
import java.util.concurrent.ConcurrentHashMap;

public class Test01 {

    public static void main(String[] args) {


        HashSet<String> set = new HashSet<>();
        HashMap<String, String> map = new HashMap<>();
        System.out.println(map);
        ConcurrentHashMap<Object, Object> map2 = new ConcurrentHashMap<>();

    }
}
